The present invention relates to an improved oven and method for hot air heating of shrink tubing and other types of items which require precise exposure to heat.
By way of background, certain manufacturing operations including those associated with the electrical, electronic and optical industries require the closely controlled application of hot air for heating various parts. A specific example is the heat-shrinking of thermoplastic tubing over wire-lugs and splices to insulate and reinforce the assemblies. The shrinkable tubing may be of any of several thermoplastic materials of various sizes, each of which has an optimum temperature and exposure time for maximum shrinkage and minimum damage.
By way of further background, the present practice for heat-shrinking tubing on wire-lug and wire-splice assemblies consists of applying air from a heat gun, hot air pencil or infrared heat gun individually to each assembly. The heat gun is generally a portable high velocity air blower with a high power heating element in the exhaust. The heat gun pulls in room temperature air and exhausts air at a temperature much higher than the optimum shrinking temperature of the thermoplastic tubing at which the heated air is directed. The higher temperature air is necessary for fast process time and to offset the cooling of the work by the ambient room air. The hot exhaust air is passed through a nozzle to provide a fast moving stream which is directed over the unshrunk tubing and the wire and lug assembly. As the tubing heats to its shrinking temperature, the operator moves the air stream relative to the work to heat the tubing on all sides for uniform shrinkage of the tubing. When the tubing has shrunk sufficiently, the work is removed from the air stream and allowed to cool. The quality of the finished assembly is highly dependent on the skill of the operator who must adjust the proximity of the nozzle relative to the work and further must direct the hot air stream around the assembly. In addition, the time that the workpiece is exposed to the hot air must be accurately gauged, as excessive heat or exposure may cause damage to either the tubing or the wire insulation. Alternatively, insufficiently exposure of heat may cause uneven or incomplete shrinkage of the tubing. Therefore the operator must develop the required degree of skill to apply the optimum temperature and time of exposure to each type of shrink tubing and other types of products.